Field of the Invention
The present invention relates to a liquid ejection head that ejects liquids such as ink, a liquid ejecting apparatus, and a method for ejecting liquids.
Description of the Related Art
In recent years, there is an increasing demand for a consumer application, in addition thereto, a business application by higher print speeds and an industrial application in regard to the inkjet technologies that eject liquids such as ink. For improving the print speed in such a liquid ejecting apparatus, a so-called full line type liquid ejection head that is configured to cause ejection openings of a liquid ejection head to correspond to a width of a print medium is preferable. For performing ejection in high landing position density of liquid droplets by such a full line type liquid ejection head, it is desirable to increase the arrangement density of the ejection openings formed in the liquid ejection head.
Japanese patent Laid-Open No. 2009-285921 is known as the configuration of such a full line type liquid ejection head that can perform a print in high density. FIG. 5 shows a part of the configuration of the liquid ejection head disclosed in Japanese patent Laid-Open No. 2009-285921. As shown in FIG. 5, a liquid ejection head 2 is provided with four ejection opening groups 121-a to 121-d. Ejection openings of each ejection opening group are arranged in a matrix on an ejection opening surface of the liquid ejection head, and positional relations between ejection opening groups are appropriately determined, thus enabling the liquid ejection head to perform printing in high density.
However, with the arrangement of the ejection openings in the liquid ejection head disclosed in Japanese patent Laid-Open No. 2009-285921, a variation in a time difference between a landing time when a liquid droplet ejected from an ejection opening lands on a print medium and a landing time when a liquid droplet ejected from the adjacent ejection opening lands on the print medium is large. As a result, there are some cases where streaks are generated in an image printed with this arrangement. Hereinafter, the mechanism of the streak generation will be explained.
For example, in a case of printing one line in a direction crossing a conveying direction of a print medium in the ejection opening arrangement having a two-dimensional structure as shown in FIG. 5, landing times of the liquid droplets, which form dots on the one line and are ejected to the print medium from the respective ejection openings, differ from each other. For this reason, a time difference between a landing time of a liquid droplet forming a certain dot and landing time of liquid droplets forming dots adjacent to one side and the other side of the certain dots differs. FIG. 12 is a graph showing an arrangement of an ejection opening and a variation in distance of the adjacent ejection opening. In FIG. 12, a position of an ejection opening on the ejection opening surface in the liquid ejection head is indicated at a black diamond shape, and a distance of the adjacent ejection opening is indicated at a black square shape. In this way, the time when the liquid droplet lands on the print medium varies due to the variation in distance between the ejection opening and the adjacent ejection opening. As a result, generating streaks caused by the liquid droplet phenomenon occur on the print medium as shown in FIG. 7. More specifically, first, a liquid droplet 130 lands on a print medium 135, a liquid droplet 131 lands thereon adjacent to the liquid droplet 130 1 msec later, and a liquid droplet 132 lands thereon adjacent to the liquid droplet 131 3 msec later. Thereafter, a liquid droplet 133 lands on the print medium after a relatively long time interval of 10 msec, but the three liquid droplets that have landed previously are contracted due to surface tension to be formed as a liquid droplet 134 having a smaller diameter. In this way, even if the liquid droplet 133 lands on the print medium adjacent to the contracted liquid droplet 134, a gap is generated between the liquid droplets without the liquid droplets coming in contact with each other, and the gap is visible as a streak on the image. This phenomenon tends to be easily generated particularly on a print medium having low absorption.